There are various dosage forms for medicines. In the case of aqueous preparations such as injections, it is desirable to put them in the form of solution, which is a final form, at a time of preparation. However, not a few medical substances are unstable in dissolved state. Therefore, such medical substances are generally dissolved at a time of use and applied, that is a dissolving method in use. Further, some medical substances cannot be obtained in crystals or are highly hygroscopic. In such cases, the medical substances are often practically used in the form of freeze-dried powder. In the case of injections, for example, a method is generally used in which freeze-dried powder is placed in a vial bottle or the like, dissolved by putting a solvent thereinto, and drawn up through an injection needle. However, it is more convenient to contain the solvent and freeze-dried powder in a syringe from the beginning. For use in a surgical operation, it is necessary to take maintenance of sterilized condition into consideration particularly.
Methods have been proposed in which a medical substance and solvent are contained in a syringe from the beginning, and dissolution is effected within the syringe immediately before use. Specifically, in such methods, a medical substance in the form of freeze-dried powder or the like is placed in the bottom of a syringe adjacent an injection needle connecting portion, and a solvent for the medical substance is placed in a plunger rod attaching portion of the syringe. The medical substance containing chamber and solvent containing chamber are partitioned in an appropriate way. The solvent and medical substance are mixed in an appropriate way for dissolution at a time of use (Japanese Patent Publication No. 50-4992, Japanese Patent Publication Kokai No. 60-72561, Japanese Utility Model Publication No. 49-14465).
However, freeze-dried powder tends to be charged with static electricity and often is in a trace quantity. Therefore, it is not easy to place the powder in the syringe accurately. In order to improve such drawbacks, it is conceivable to carry out freeze-drying in the syringe. Usually the syringe has an inner wall coated with a silicone oil solution having a concentration of 1-5% (W/V) in order to enable smooth movement of gaskets and a plunger rod in use. A solution of medicine becomes turbid when freeze-dried after placement in a silicone-coated syringe in the above concentration and then redissolved as a freeze-dried powder in a solvent. The product is then not suitable as a medicine.
On the other hand, in a known form of such a two-compartment syringe, gaskets are used to partition between the powder containing chamber and solvent containing chamber and between the solvent containing chamber and ambient air, respectively, as in the publications noted above. However, there is a risk that expansion of interior air in the powder containing chamber is caused by an increase of temperature, and pushes up the gaskets, whereby the gaskets fall off. A syringe is also known which includes a flange-like finger hook formed integral with an outer peripheral surface thereof for pushing in the plunger rod to mix the powder and solvent and to push the solution out of the syringe.
However, a two-step operation is necessary with a two-compartment syringe, and there has been a problem in securely supporting the syringe to give an injection to an affected organ exactly.
The objects of the present invention are to provide a two-compartment syringe capable of suppressing turbidity occurring when freeze-dried powder is dissolved in a solvent to a degree not obstructive to use while maintaining movement of the gaskets and plunger rod in a smooth condition with silicone coating applied to the inner wall of the syringe. A further object of the present invention is to provide a two-compartment syringe having excellent operability and devised to be capable of preventing the gaskets from falling off caused by air expansion in the powder containing chamber and capable of mixing the powder and solvent. Another object is to provide a syringe for injecting the resulting liquid mixture easily and accurately.